Equipment condition and performance monitoring using comprehensive process model based upon mass and energy conservation

ABSTRACT

A method and apparatus capable of monitoring performance of a process and of the condition of equipment units effecting such process is disclosed. A process model predicated upon mass and energy balancing is developed on the basis of a plurality of generally nonlinear models of the equipment units. At least one or more of such equipment models are characterized by one or more adjustable maintenance parameters. Data relating to mass and energy transfer within the process is collected and is reconciled with the mass and energy characteristics of the process predicted by the model. The condition of the equipment units and process performance may then be inferred by monitoring the values of the maintenance parameters over successive data reconciliation operations.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 60/338,052, filed Nov. 30, 2001,which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of equipment condition andprocess performance monitoring and, in particular, to systems andmethods for monitoring such condition and performance using datareconciliation techniques predicated upon mass and energy conservation.

BACKGROUND OF THE INVENTION

Complex industrial systems such as, for example, power generationsystems and chemical, pharmaceutical and refining processing systems,have experienced a need to operate ever more efficiently in order toremain competitive. This need has resulted in the development anddeployment of process modeling systems. These modeling systems are usedto construct a process model, or flowsheet, of an entire processingplant using equipment or component models provided by the modelingsystem. These process models are used to design and evaluate newprocesses, redesign and retrofit existing process plants, and optimizethe operation of existing process plants.

Existing flowsheet modeling techniques have been directed to discreteunits of plant equipment, rather than to entire plant processes. Incertain approaches the operation of individual items of plant equipmentpredicted by a flowsheet model is attempted to be reconciled withmeasurements of the equipment's actual operation. Data relating to suchactual operation is typically acquired by flow sensors and the likepositioned on or near the item of equipment. Such flow sensors vary intheir accuracy depending on the material in the stream being monitored,the condition of the stream, and the specific sensing technologyemployed within the flow sensor. Moreover, the performance of flowsensors may be degraded by obstructions, wear or outright failure. Theattendant inaccuracies in the operational data produced by the flowsensors may corrupt the reconciliation of such data with the equipmentperformance predicted by the flowsheet model, thereby resulting inundesirable erroneous predictions or process control adjustments.

The data reconciliation process often involves minimization of the sumof squared errors between predicted and measured operational parameters.However, the relative accuracy of the sensors used in deriving the errorterms is generally not taken into account, which tends to introduceinaccuracies into the reconciliation process. That is, a sensor whosebehavior changes due to failure or deterioration may cause incorrectadjusted estimates to be attributed to related sensors during thereconciliation process. Since conventional flowsheet models are notpredicated upon operation of entire plant processes, it can be difficultto gauge when predicted operation of individual equipment isinconsistent with realistic operation of an overall process.

Equipment condition has also been attempted to be monitored usingflowsheet models directed to individual units of equipment. However, itis generally difficult to determine whether a change in output or othermonitored parameter of an individual unit of equipment is properlyattributed to a change in the equipment itself or to a change in theapplicable process “upstream” of the equipment unit.

In the field of power generation systems, this limitation of existingmodeling techniques has proven to be particularly undesirable asconcerns with deregulation and operational costs have resulted inefforts to improve system reliability and performance. As is well known,the Rankine cycle power plant, which typically utilizes water as theprocessed fluid, has been pervasive in the power generation industry formany years. In a Rankine cycle power plant, electrical energy is derivedfrom heat energy through the heating of the processed fluid as ittravels through tubular walls and thereby forms a vapor. The vapor isgenerally superheated to form a high pressure vapor, which is input to aturbine generator to produce electricity.

Other improvements in the efficiency of Rankine cycle power systems havebeen achieved through technological enhancements, which have enabled thetemperatures and pressures of processed fluids to be increased. Whenreconciliation techniques such as those described above are employed tomonitor the performance of such power systems, such techniques are oftenapplied to individual units of equipment or indicia of performance(e.g., turbine efficiency). A dramatic change in such indicia signalsthat the applicable unit(s) of equipment may be not be operatingproperly. Again, however, such approaches are premised upon models ofonly subsets of the equipment utilized in the overall power generationprocess, and thus are not subject to the constraints which could beimposed upon the Rankine cycle of the process. This makes suchapproaches inherently uncertain, because it will not be known whetherchanges in monitored parameters of isolated equipment units are due toequipment degradation or to changes in upstream conditions.

SUMMARY OF THE INVENTION

In general, the present invention relates to a method and apparatuscapable of monitoring performance of a process and of the condition ofequipment units effecting such process. A process model predicated uponmass and energy balancing is developed on the basis of a plurality ofgenerally nonlinear models of the equipment units. At least one or moreof such equipment models are characterized by one or more adjustablemaintenance parameters. As is described below, data relating to mass andenergy transfer within the process is collected and is reconciled withthe mass and energy characteristics of the process predicted by themodel. In accordance with one aspect of the invention, the condition ofthe equipment units and process performance may be inferred bymonitoring the values of the maintenance parameters over successive datareconciliation operations.

In a particular aspect the present invention relates to a method formonitoring the condition of a plurality of units of equipment used toeffect a process involving one or more resource flows of mass andenergy. The method includes measuring one or more quantities related tothe resource flows (e.g., temperature, pressure, flow rate) in order togenerate respective first and second measured resource flows. A model ofthe process is formulated so as to include a plurality of generallynonlinear equipment models corresponding to the plurality of units ofequipment, wherein at least a first of the nonlinear equipment modelsincludes a first maintenance parameter. A value of at least the firstmaintenance parameter is adjusted such that predictions of the flowrates are reconciled with the first and second measured resource flows.In addition, changes in the value of the first maintenance parameter areadjusted over time in order to enable detection of changes in thecondition of at least one of the plurality of units of equipment.

In another aspect, the present invention relates to a method ofprocessing signals representative of a process effected by one or moreequipment units in operative communication through one or more resourceflows. The method includes measuring flow rates of at least first andsecond of the resource flows in order to generate respective first andsecond measured resource flow signals. A model of the process isformulated based upon conservation of a process parameter characterizingthe first and second resource flows, wherein the model includes at leasta first maintenance parameter. The method further contemplates adjustinga first value of the first measured resource flow signal, a second valueof the second measured resource flow signal, and the first maintenanceparameter such that the process parameter is conserved consistent withthe model.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature of the features of theinvention, reference should be made to the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustratively represents the network architecture of a systemwithin which one embodiment of the present invention may beincorporated.

FIG. 2 illustrates an architecture of a client unit which may be usedwith an exemplary embodiment of the present invention.

FIG. 3 is a block diagram representative of the internal architecture ofa server unit operative in accordance with the present invention.

FIG. 4 further illustrates certain additional components comprising amodeling engine of a simulation module.

FIG. 5 further illustrates one embodiment of the interaction between themodeling engine and a solution engine of the simulation module.

FIGS. 6-9 illustratively represent a mathematical basis for a datareconciliation operation performed in accordance with one aspect of thepresent invention.

FIG. 10 depicts a relationship of the data reconciliation module toother system functionality within a general process control system.

FIG. 11 provides a high-level illustrative representation of theoperation of a simulation module.

FIG. 12 provides a high-level illustrative representation of theoperation of an optimization module.

FIG. 13 illustratively represent one manner in which instrument errorsand component degradation may be identified in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustratively represents the network architecture of a system100 within which one embodiment of the present invention may beincorporated. The system operates on a process 101, which may compriseany process including, without limitation, chemical processes, energyprocesses and distribution processes. In the case of a process 101geared toward power generation, the math model will preferably reflectthe Rankine cycle of the power generation operation. In implementationsinvolving chemical and other processes, the material in the process canbe treated as a fluid that is moved within the process in streams. Aprocess is normally made up of more than one unit of equipment, whereeach unit carries out some specific processing function, such asreaction, distillation, or heat exchange. Equipment units areinterconnected and/or in fluid communication via streams. A plurality ofplant sensors 107 are selected and configured to measure values of theregulatory variables applicable to the equipment units used to performthe process 101. These regulatory variables, e.g., pressure,temperature, level, and flow, are controlled to maintain processequipment operating at a designated stationary state. These variablesmay also be adjusted by the operator to move the process equipment toanother stationary state (e.g., to increase production).

As is described below, in one aspect the method of the present inventioncontemplates reconciling predicted operation of an entire plant processand data measured by plant sensors 107. In this regard the inventivemethod forces reconciliation of such measured plant data and predictedoperational data derived from a comprehensive model of the entire plantprocess based upon generally nonlinear models of individual units ofequipment. Each such nonlinear model is characterized by one or moreparameters, some or all of which are designated as maintenanceparameters. The maintenance parameters associated with the model of aparticular unit of equipment will generally be selected so as to bereflective of the “health” or operational soundness of the equipmentunit. For example, one of the maintenance parameters for aheat-exchanger could be a heat transfer coefficient while one of themaintenance parameters for a pump could be a pump curve scaling factor.

In an exemplary embodiment reconciliation between the plant operationpredicted by the comprehensive plant model and the measured plant datais effected so as to establish an overall mass and energy balance. Thisapproach is believed to be different from prior techniques, which havetended to be confined to optimization of discrete portions of an overallplant process without regard to maintenance of overall mass and energybalance. In an exemplary embodiment, the result of the reconciliationprocess of the present invention transforms the signals generated by theplant sensors into corrected measurement signals and adjusts the valuesof maintenance parameters within predefined ranges based upon estimatedequipment variances.

Such simultaneous modification of both measured values and maintenanceparameters over an entire process is believed to represent a significantdeparture from prior reconciliation techniques.

It has also been found that the changes in maintenance parameters acrosssuccessive reconciliation operations may provide an indication of thecondition of the equipment unit with which the maintenance parameter isassociated. Such monitoring of maintenance parameters over time isbelieved to represent a novel approach to gauging equipment condition.This approach is facilitated by utilization of a comprehensive plantmodel comprised of a set of generally nonlinear models of individualequipment models. Prior modeling techniques involving only a portion ofa plant process would not enable meaningful information to be gleanedfrom such monitoring of maintenance parameters over time, since it wouldbe unclear as to whether changes in the monitored maintenance parameterswere due to deterioration in equipment condition or to changes inupstream process conditions.

The system 100 may include a local area network (LAN) 102 that isconnectable to other networks 104, including other LANs or portions ofthe Internet or an intranet, through a router 106 or similar mechanism.One example of such a LAN 102 may be a process control network to whichprocess control devices, such as process controller 114, and plantsensors 107 are connected. Process control networks are well known inthe art and are used to automate industrial tasks. The network 104 maybe a corporate computing network, including possible access to theInternet, to which other computers and computing devices physicallyremoved from the process 101 are connected. In one embodiment, the LANs102, 104 conform to Transmission Control Protocol/Internet Protocol(TCP/IP) and Common Object Request Broker Architecture (COBRA) industrystandards. In alternative embodiments, the LANs 102, 104 may conform toother network standards, including, but not limited to, theInternational Standards Organization's Open Systems Interconnection,IBM's SNA®, Novell's Netware®, and Banyon VINES®.

The system 100 includes a server 108 that is connected by network signallines to one or more clients 112. In an exemplary embodiment the server108 includes a UNIX or Windows NT-based operating system. The server 108and clients 112 may be uniprocessor or multiprocessor machines, and mayotherwise be configured in a wide variety of ways to operate consistentwith the teachings of the present invention. The server 108 and clients112 each include an addressable storage medium such as random accessmemory and may further include a nonvolatile storage medium such as amagnetic or an optical disk.

The system 100 also includes a storage medium 110 that is connected tothe process control network 102 or corporate control network 104. In theexemplary embodiment the storage medium 110 may be configured as adatabase from which data can be both stored and retrieved. The storagemedium 110 is accessible by devices, such as servers, clients, processcontrollers, and the like, connected to the process control network 102or the corporate control network 104.

Suitable servers 108 and clients 112 include, without limitation,personal computers, laptops, and workstations. The signal lines mayinclude twisted pair, coaxial, telephone lines, optical fiber cables,modulated AC power lines, satellites, and other data transmission mediaknown to those of skill in the art. A given computer may function bothas a server 108 and as a client 112. Alternatively, the server 108 maybe connected to the other network 104 different from the LAN 102.Although particular computer systems and network components are shown,those of skill in the art will appreciate that the present inventionalso works with a variety of other networks and components.

FIG. 2 illustrates an architecture of the client 112 which may be usedwith one preferred embodiment of the present invention. The client 112provides access to the functionality provided by the server 108. Theclient 112 includes a GUI 202 and an optional module interface 204. TheGraphical User Interface (GUI) 202 is used to build and specify modelapplications. One embodiment of the GUI 202 incorporates user interfacefeatures such as tree views, drag-and-drop functionality, and tabbedwindows to enhance the intuitiveness and usability of the interface. TheGUI 202 further enables access to other encapsulated GUIs such asprocess unit GUIs, non-process unit GUIs, and stream GUIs as describedbelow.

Access to the GUI 202, as well as other architectural objects to bediscussed in detail below, are through the optional module interface204. In one embodiment, the module interface 204 is the InterfaceDefinition Language (IDL) as specified in the CORBA/IIOP 2.2specification. In one embodiment, the module interface 204 provides auniform interface to the architectural objects, such as the GUI 202. Themodule interface 204 allows the actual implementation of thearchitectural objects, such as the GUI 202, to be independent of thesurrounding architecture, such as the operating system and networktechnology. One of ordinary skill in the art will recognize that themodule interface 204 may conform to other standards, or even benon-existent.

FIG. 3 is a block diagram representative of the internal architecture ofthe server 108, which may be physically implemented using a standardconfiguration of hardware elements. As shown, the server 108 includes aCPU 330, a memory 334, and a network interface 338 operatively connectedto the LAN 102. The memory 334 stores a standard communication program(not shown) to realize standard network communications via the LAN 102.The memory 334 further stores a solver 302 accessible by a modelingengine 304 through an access mechanism 306, and a modeling engineframework 308. The solver, modeling engine 304, and modeling engineframework 308 collectively comprise a simulation module 340, theoperation of which is further described below. The optional moduleinterface 204 provides uniform access to, and implementationindependence and modularity for both the modeling engine 304 and themodeling engine framework 308. As is discussed below, the memory 334also stores a data reconciliation module 350 containing a set ofcomputer programs which, when executed, effect certain mass and energybalance reconciliation processes of the present invention.

The modeling engine 304 provides an environment for building and solvingprocess models. The solver 302 provides a solution algorithm for solvinga process model generated by the underlying modeling engine 304. In oneembodiment, the solver 302 may contain one or more solution engines 310which are used in solving different process models. For example, onesolver that may be used is Opera, a solver available from the SimulationSciences unit of Invensys Systems, Inc. as part of the ROMeo System. Inone embodiment, the solver 302 comprises a solution engine 310implemented as a generalized matrix solver utilizing a Harwellsubroutines. As is well known in the art, the Harwell library is anapplication independent library of mathematical subroutines used insolving complex mathematical equation sets. In one embodiment, theaccess mechanism 306 is specific to the solution engine 310 contained inthe solver 302 and the modeling engine 304 used in generating the mathmodel.

The modeling engine framework 308 is an interpretive layer providinguser-friendly access to the modeling engine 304. In one embodiment, themodeling engine framework 308, working in conjunction with the GUI 202,provides a user the ability to add new unit models, modify existing unitmodels, and generally interact with the modeling engine 304 withouthaving to know the specifics of the modeling engine 304.

FIG. 4 further illustrates certain additional components comprising themodeling engine 304 in one preferred embodiment. The modeling engine 304comprises model elements 402, a flowsheet manager 404, and an eventhandler 406. The model elements 402 include individual units and streamsfrom which a user builds a flowsheet model. For example, a pump is aunit that the user may include in a flowsheet model.

A unit represents a device that may be found in a process plant. Theunit may be a process or an on-process unit. A process unit is an itemof operating hardware such as a heat exchanger, a compressor, anexpander, a firebox, a pipe, a splitter, a pump, and the like. Asmentioned above, each unit is represented by a generally nonlinear modelcharacterized by one or more parameters. Each parameter of a given modelwill typically pertain to mass or energy transfer characteristics of theequipment unit represented by the model. Some or all of these parametersmay be considered maintenance parameters, and will generally beconsidered as such to the extent that monitoring the changes in theirrespective values over time may enable inference of the condition of theapplicable unit of equipment.

A non-process unit is something other than an item of operatinghardware. For example, a non-process unit may be a penalty. A penaltyunit assigns a progressively increasing weight to a measured outputtemperature value beyond the optimum output temperature. For example,the penalty unit may account for the increased cleanup costs associatedwith operating the furnace at a higher than optimum output temperature.Another example of a non-process unit may be a measurement frommeasuring devices such as flow meters, thermocouples, and pressuregauges.

In one embodiment, each unit typically has one or more entry or exitports and is associated with a model. The model is a collection ofvariables and equations, collectively known as a calculation block. Aunit model represents the operation of the unit in terms of itsassociated calculation block. As an example, an equation for ameasurement unit may be:

ModelVariable−Scan−Offset==0

where ModelVariable is a calculated value, Scan is a measured value, andOffset is the difference between ModelVariable and Scan. The aboveequation contains three variables: ModelVariable, Scan and Offset.

As another example, the equations for a pump unit may be:

PresRise−Product:Pres+Feed:Pres==0, and

Head*GravConst*Feed:Prop[“WtDens”]1000*PresRise==0

where PresRise is a rise in pressure, Product:Pres is an outputpressure, Feed:Pres is an input pressure, Head is a liquid height withina tank connected to the pump, GravConst is the gravity constant,Feed:Prop[“WtDens”] is a weight density of the liquid in the tank, andthe PresRise is a rise in pressure of the pump. In the first equation,PresRise, Prod:Pres, and Feed:Pres are variables. In the secondequation, Head, Feed:Prop[“WtDens”], and PresRise are variables.GravConst is a parameter, and thus requires a value to be assignedbefore the equation may be solved.

A stream is used to connect a unit's entry or exit port to anotherunit's exit or entry port respectively. Furthermore, a feed stream isconnected to the unit's entry port, whereas a product stream isconnected to the unit's exit port. A stream model may have associatedequations and variables. For example, a simplified stream model may berepresented as follows:

y=ax+b

where “y” is a measurement that is allowed to assume values within apredefined range, and “x”, “a” and “b” are parameters representative ofequipment condition (i.e., “a” and “b” will generally change over timedue to equipment wear), and “x” is a calculated value. During thereconciliation operation, the values of “y”, “a” and “b” and similarvalues within all other equipment models of the applicable process areallowed to change until the overall process model reflects that mass andenergy balance has been achieved throughout the process.

In one exemplary embodiment, multi-dimensional data structures are usedto store individual units and streams, and their associated variablesand equations. The data structures may also store other information suchas, but not limited to, the type of unit or stream, whether a variablerequires a user-provided value, the variable's lower bound, upper bound,solution value, or status. One of ordinary skill in the art willrecognize that the data structures may be in the form of an array,linked list, or as elements within other data structures.

The flowsheet manager 404 provides access to instances of unit models,stream models, and other information associated with a flowsheet model.In one embodiment, the information associated with a flowsheet model maybe stored in the storage medium 110. Preferably, the storage medium 110stores at least one flowsheet model, including an equation, of an actualplant process. The flowsheet manager 404 may then communicate with thestorage medium 110 to provide a user access to the information containedin the storage medium 110 in a manageable format. Further detailsregarding creation, modification and alteration of flowsheet models areprovided in, for example, copending U.S. patent application Ser. No.09/193,414, filed Nov. 17, 1998 and entitled INTERACTIVE PROCESSMODELING SYSTEM; U.S. Pat. No. 6,442,515, which is entitled PROCESSMODEL GENERATION INDEPENDENT OF APPLICATION MODE; and U.S. Pat. No.6,323,882, which is entitled METHOD AND SYSTEMS FOR A GRAPHICAL REALTIME FLOW TASK SCHEDULER, each of which is hereby incorporated byreference in its entirety.

FIG. 5 further illustrates one embodiment of the interaction between themodeling engine 304 and the solution engine 310 of the simulation module340. As is described in the above copending patent applications, themodeling engine 304 additionally comprises a model generator 502, aresidual generator 504, and a derivative generator 506. The modelingengine 304 provides the open form of model equations to the solutionengine 310. The solution engine 310, in turn, solves the equations. Inan alternative embodiment, a closed form of the model equations may beprovided by the modeling engine 304.

The model generator 502 creates a math model of the flowsheet for inputto the solution engine 310. In the exemplary embodiment, the math modelis a large set of equations and variables that comprehensively modelsthe entire process 101. The math model will typically be in the form ofa matrix which represents the equations contained in the flowsheet modelin the form f(x)=0. Standard equations and variables associated with acorresponding unit model or stream model are provided in a previouslycompiled standard library 508. The equations may comprise mass,material, equilibrium, thermodynamic, and physical property relatedequations applicable to the process 101 in its entirety.

As is described below, the data reconciliation module 350 uses the mathmodel and measurements from the sensors 107 in computing reconciledmodel parameters and sensor measurements capable of being used to effectclosed loop control of the process 101. This computation is effected byadjusting (within the range of sensor accuracy) the measurements fromthe sensors 107 and the parameters of the math model until a solution isdetermined.

Again, in the exemplary embodiment the math model reflects mass andenergy balance throughout the process 101 in its entirety; that is, themath model takes into account substantially all of the mass and energyassociated with the process 101. This is effected in part by specifyingthe input and output relationships with respect to mass and energy foreach equipment model. In addition, equality constraints are applied asappropriate to those models representative of equipment units betweenwhich mass/energy is transferred. As a consequence, the datareconciliation module 1022 operates upon a set of equations whichcharacterize mass and energy flow for the entire process 101. Thisdiffers from conventional approaches, in which mass and/or energybalance is computed on only a localized basis.

The exemplary embodiment also contemplates that the accuracy of everysensor 101 used to measure parameters associated with the process 101 ischaracterized. This characterization generally involves determining thevariance of each sensor 107, which reflects the range over which thevalue of the variable measured by the sensor 107 can vary during thereconciliation process and still be consistent with expected calibrationaccuracy. Determination of the variance of each sensor 107 thusfacilitates identification faulty or malfunctioning sensors, since anadjustment in the value of the sensor during the reconciliation processoutside of such variance indicates that the sensor has been providing anerroneous measurement value. Similarly, variances are ascribed to one ormore parameters associated with each model element 402 representative ofa unit of equipment or characteristic of the process 101. If adjustmentsmade to such parameters during the reconciliation process result inostensible operation of a unit of equipment outside of an expectedrange, then there exists a substantial likelihood of significantequipment degradation or malfunction. The present invention thusadvantageously facilitates identification of faulty or inoperative unitsof equipment contributing to operation of the process 101.

FIGS. 6-9 provide an illustrative representation of a mathematical basisfor a data reconciliation process effected in accordance with thepresent invention. Turning to FIG. 6, there is shown a simplified flowsystem 600 having an input flow stream 602 designated as relating inwhat follows to a mathematical variable X3. As shown, the simplifiedflow system 600 includes first and second output flow streams 604 and608 designated as relating to the mathematical variables X1 and X2,respectively. The discussion below is intended to elucidate a number ofmathematical concepts underlying various features of the presentinvention.

Although the flow streams represented by FIG. 6 will often be associatedwith mass or matter in “bulk”, the streams could also representative ofa thermodynamic quantity (e.g., energy) or a specific component of amaterial being processed. As shown, the first flow stream 602 isseparated into the second and third flow streams 604 and 608 at aprocess node 612. Depending upon the context of the flow system 600, thenode 612 may correspond to various physical realizations (e.g., athree-way connector). Although the node 612 may operate to maintain asubstantially constant rate of flow, in a more complex arrangement thenode 612 may be representative of an overall process effected by aplurality of components. In the latter case, the sum of the flows of theoutput flow streams 604 and 608 may not equilibrate with the flow of theinput flow stream as frequently as in simpler manifestations of the node612.

In the case when the node 612 is implemented straightforwardly topartition the input flow stream 602, conservation of mass requires that

X ₁ +X ₂ −X ₃=0   Equation (1)

In order to account for the possibility of a nonlinear relationshipbetween the input flow stream 602 and the output flow streams 604 and608, the output flow streams 604 and 608 may be expressed as function ofparameters P1 and P2 as follows:

X ₁ =F1(P1, X ₃)   Equation (2)

X ₂ =F2(P2, X ₃)   Equation (3)

In equations (2) and (3) the functions F1 and F2 could, for example,represent valve curves dependent upon the parameters P1 and P2.

Referring again to Equation (1), when actual measured values X′₁, X′₂,and X′₃ of the three flows X₁, X₂, and X₃ are utilized it is likely thatmass will not be conserved and Equation (1) will not be satisfied. Ingeometric terms, the measurements X′₁, X′₂, and X′₃ may be considered todefine a point in space while equation (1) may be viewed as defining aplanar surface. That is, all sets of flows X₁, X₂, and X₃ in the planesatisfy equation (1). Any given set of measured flows values X′₁, X′₂,and X′₃ will generally not conserve mass, and hence will generallyspatially correspond to a point outside of the plane.

Turning now to FIG. 7, the process of data reconciliation in accordancewith the present invention is illustratively represented in geometricterms. As shown, a point P_(N) defined by a measured set of flows X′₁,X′₂, and X′₃ is translated from a location out of a plane P of flowvalues X₁, X₂, and X₃ satisfying equation (1). Although in the contextof FIG. 7 this translation is effected by simply adjusting theparameters the values of the measured flows X′₁, X′₂, and X′₃, in anexemplary embodiment both the parameters P1 and P2 of Equations (2) and(3) and the values of the measured flows X′₁, X′₂, and X′₃ are adjustedin order to move the point P_(N) into the plane P. Once point P_(N) hasbeen translated onto the plane P, it may be characterized as having beenreconciled (i.e., the measured values X′₁, X′₂, and X′₃ and parametersP1 and P2 have been modified to the extent necessary to satisfyEquations (1)-(3)). Mathematically, this reconciliation process may beequivalently represented as the determination of an offsetreconciliation vector V1 and its addition to the vector extendingbetween the origin and the point P_(N).

FIG. 8 represents the manner in which a set of measured flow values maybe reconciled either through a least squares minimization process inwhich both the parameters P1 and P2 and measured flow values arethemselves adjusted. As shown, at a time t₁ a set of reconciled flowsmay exist which define a point P_(R, t1) on the plane P of flow valuessatisfying equation (1). At a subsequent point in time (t₂), a set ofmeasured flows X′_(1, t2), X′_(2, t2), and X′_(3, t2) are seen to definea point P_(M, t2) off of the plane P. In accordance with the invention,the values of the parameters P1 and P2 and the values of the measuredflows X′_(1, t2), X′_(2, t2), and X′_(3, t2) are each modified to theextent of the uncertainty inhering in each such value until the pointP_(M, t2) is “translated” to the plane P. This reconciliation may beeffected in accordance with the least-squares expression of equation(4), which in the exemplary implementation is minimized throughperturbation of both measured values X′ and model parameters:

$\begin{matrix}{{\underset{\begin{matrix}{{{Tuning}\mspace{14mu} {Parameters}}\mspace{14mu}\&} \\{{Measured}\mspace{14mu} {Values}}\end{matrix}}{Min}{{Offset}}^{2}} = {{{\underset{\_}{X^{\prime}} - \underset{\_}{x}}}^{2} = {{\frac{1}{\sigma_{1}^{2}}\left( {X_{1}^{\prime} - x_{1}} \right)^{2}} + {\frac{1}{\sigma_{2}^{2}}\left( {X_{2}^{\prime} - x_{2}} \right)} + {\frac{1}{\sigma_{3}^{2}}\left( {X_{3}^{\prime} - x_{3}} \right)^{2}}}}} & {{Equation}\mspace{14mu} (4)}\end{matrix}$

where the weighting factor, a, present in Equation (4) takes intoaccount both the uncertainty and inaccuracy in the measured values X′ ofthe sensors 107 and in the parameters (i.e., P1, P2 of Equations (2) and(3)) associated with the model elements 402. In particular, uncertaintyin the readings from the sensors affects the value of X′ within eachoffset term, while uncertainty in the values of the parameters affectsthe value of x within each offset term. The least squares objectivefunction illustrated of Equation (4) is formulated such that eachindividual offset (i.e., (X′₁−x₁)², (X′₂−x₂)², (X′₃−x₃)²) is multipliedby the reciprocal of the standard deviation (or variance) obtainedduring steady state conditions from a historical set of data for therelevant measured data value. The approach exemplified by Equation (4)aids in reducing the predictable noise effects introduced by theuncertainty and/or inaccuracy inherent with the sensors 107 or equipmentmaintenance parameters.

In the exemplary embodiment, Equation (4) is solved under conditions of“steady state” operation. “Steady state operation” essentiallycorresponds to the case where (1) a process is substantially regular anduniform in its operation over a given time interval, (2) momentum, mass,and energy entities flowing into the process are substantially equal tothe momentum, mass, and energy entities flowing out of the process, and(3) momentum, mass, and energy do not otherwise accumulate within theprocess unless stipulated by the relevant equipment model.

FIG. 9 illustratively represents a process of successive reconciliationin accordance with the present invention. As shown, at a time t₀ a setof reconciled flows (x₁, x₂, x₃) may exist which define a pointP_(R, t0) on a plane P1 of flow values satisfying equation (1). That is,

x ₁ +x ₂ −x ₃   Equation (5)

where,

x ₁ =F1(p ₁)   Equation (6)

x ₂ =F1(p ₂)   Equation (7)

x ₃ =F1(p ₃)   Equation (8)

At a subsequent point in time (t₁), a set of measured flows X′_(1, t1),X′_(2, t1), and X′_(3, t1) are seen to define a point P_(M, t1) off ofthe plane P1. Consistent with the invention, the values of theparameters p₁, p₂ and p₃, as well as the values of the measured flowsX′_(1, t1), X′_(2, t1), and X′_(3, t21) are modified by the simulationmodule 340 to the extent of their respective uncertainties until thepoint P_(M, t1) defines a point (P_(R, t1)) on the plane P1. As notedabove, this reconciliation may be effected in accordance with theleast-squares expression of equation (4). As a consequence of thisreconciliation, the model parameters p₁, p₂ and p₃ are incremented bythe quantities dp₁, dp₂ and dp₃, respectively, thereby yielding modifiedmodel parameters as of time t₁:

p′ ₁ =p ₁ +dp ₁

p′ ₂ =p ₂ +dp ₂

p′ ₃ =p ₃ +dp ₃

As shown in FIG. 9, at later point in time (t₂) a set of measured flowsX′_(1, t2), X′_(2, t2), and X′_(3, t2) are seen to define a pointP_(M, t2) off of the plane P1. The values of the parameters p′₁, p′₂ andp′₃, as well as the values of the measured flows X′_(1, t2), X′_(2, t2),and X′_(3, t22) are then modified by the simulation module 340 asdescribed above until the point P_(M, t2) defines a point (P_(R, t2)) onthe plane P1.

In accordance with one aspect of the invention, the behavior of theparameters p₁, p₂, and p₃ over time (e.g., days and months) can bemonitored in order to detect equipment wear and enable anticipation ofprobable equipment failure. In particular, certain equipment parametersare identified as maintenance parameters and set as “free variables” tobe monitored over time. The observed changes in these maintenanceparameters may then provide an indication of equipment deterioration orimminent failure. In general, the maintenance parameters will beselected from among those equipment model parameters indicative of thecapability of a given equipment unit to conduct mass and energy asintended. Significant changes in the values of such parameters as aresult of the reconciliation process will generally be indicative of anadverse change in the state of the applicable equipment.

FIG. 10 depicts the relationship of the data reconciliation module 1022to other system functionality within a general process control system1000. In specific embodiments the control system 1000 may be utilized inthe control of, for example, power generation processes, chemicalprocesses, refineries and transportation systems. The material operatedupon by the process can often be treated as a fluid, which are movedwithin the process in streams. A process is typically comprised ofmultiple elements connected by way of streams. Each element effects acertain function (e.g., reaction, distillation, or heat exchange).

Referring to FIG. 10, the data reconciliation module 1022 operatestogether in a system 1000 with a set of regulation devices 1004 underthe control of the process controller 114. The regulation devices 1004and the process controller 114 collectively control equipment-relatedvariables such as pressure, temperature, level, and flow (commonly knownas “PTLF” variables) in order to maintain the process 101 in a certaindesired state. In particular, the regulation devices 1004 respond tooutput signals from the process controller 114 to produce an accordinglypredetermined operation representing the strength of the output signal.Both the process controller 114 and PTLF-based regulation devices 1004are familiar to those skilled in the art. The values of various PTLFvariables may be adjusted in an operator setpoint adjustment operation1010 in order to move the equipment involved in the process 101 toanother stationary state.

In the controlled system 1000 of FIG. 10, various aspects of the process101 are monitored by the sensors 107. To this end, the sensors 107produce output signals representative of the values of various PTLF orother characteristics of the process 101. The output signals from thesensors 107 correspond to process variables operated upon by the system1000. Based upon these output signals, a steady state detectionoperation 1014 determines when the process 101 enters a steady statecondition (described above). Once a steady-state condition has beenachieved, the raw sensor output signals are screened against the upperand lower limits defining predefined acceptable ranges in a screenmeasurements operation 1018. In a particular implementation defaultvalues may be substituted for those raw sensor signals discarded duringthe screen measurements operation 1018. The remaining sensor outputsignals, and any substituted default signals, are then processed in thedata reconciliation module 1022.

The data reconciliation module 1022 utilizes the sensor signals from thescreen measurements module 1018 and predicted process data provided bythe simulation module 340 in creating reconciled measurement signals forutilization during a subsequent optimization operation 1026. Thepredicted operational data (e.g., pressure, level, temperature, andflow) created by the simulation module 340 is generated by the solver302 on the basis of the model of the process 101 established by themodeling engine 304. Prior to performing the optimization operation1026, the reconciled measurement data generated by the reconciliationmodule 1022 is communicated to a constraint projection module 1030. Thereconciliation operation effected by the reconciliation module 1022results in creation of an improved set of process measurement data foruse during the optimization operation 1026, thereby reducing thelikelihood of inappropriate control of the process 101.

FIG. 11 provides a high-level illustrative representation of theoperation of the simulation module 340. As is illustrated by FIG. 11,the simulation module 340 may also be utilized to simulate the state ofthe process 101 in response to varying load conditions and setpoints ofthe regulation devices 1004. As mentioned above, in the exemplaryembodiment the data reconciliation module 1022 provides updated modelparameters and data to the simulation module 340 at the conclusion ofeach data reconciliation operation (step 1102 of FIG. 11). This is donein order to cause the simulation model 340 to more accurately predictthe characteristics of the process 101 measured by the sensors 107.Periodic calibration of the model parameters (step 1106) compensates forchanges in the behavior of the process 101 relative to the simulatedoperation computed by the simulation module 340. This enables thesimulation results produced by the simulation model 340 to be refined asits model parameters are periodically adjusted in connection with eachiteration of the data reconciliation module 1022. Various “what if”scenarios may then be investigated by adjusting parameters (e.g.,ambient conditions, set-point, and process load) associated with thesimulation model 340 (step 1110). In particular, simulated data underthese new ambient conditions and/or set points is then produced by thesimulation model 340 and may be reported to operators of the process 101(step 1114).

Referring again to FIG. 10, the reconciled process measurement data isprocessed during the optimization operation 1026 upon being furnished bythe constraint projection module 1030. In the exemplary embodiment theoptimization operation 1026 is also comprised of the modeling engine 304and the solver 302. That is, the mass and energy balance equationsincorporated within the modeling engine 304 may also be used foroptimization after undergoing the reconciliation effected by the datareconciliation module 1022.

FIG. 12 provides a high-level illustrative representation of anexemplary optimization operation 1026. In a step 1202, the variables ofthe applicable mass and energy balance equations are initialized withvalues generated during a prior iteration of the simulation module 340.A cost-based objective function is then formulated in which certain ofthese variables of interest are set to an independent state (step 1206).The independent variables are then incremented until the cost-basedobjective function is minimized (step 1210), and the operational resultsreported (step 1214).

FIG. 13 illustratively represent one manner in which instrument errorsand component degradation may be identified through use of a datareconciliation module 1022 in accordance with the present invention. Asis illustrated by FIG. 13, in a step 1302 the variables of the mass andenergy balance equations included within the data reconciliation module1022 are set in accordance with measurements of the parametersapplicable to the monitored process. A weighted least squares (WLS)objective function is then formulated in which various parameters of theapplicable equipment models (i.e., the equipment maintenance parameters)are set to a default state (step 1306). As mentioned above, themaintenance parameters associated with a particular unit of equipmentwill generally be selected to be parameters to reflective of the“health” or operational soundness of the equipment unit. By monitoringthe change in such maintenance parameters over time it is thus possibleto monitor the condition of selected units of equipment. In this wayequipment maintenance or replacement may be scheduled when a change inthe maintenance parameter(s) for a particular unit of equipment indicatethat the equipment has experienced degradation or is likely to fail ormalfunction.

Referring again to FIG. 13, the parameters characterizing the monitoredprocess (including the maintenance parameters) are incremented until theWLS objective function is minimized (step 1310), and the reconciled datareported (step 1314). In addition, an instrument error report may begenerated when the values of one or more maintenance or other parametersassociated with an equipment unit diverge from one or more correspondingpredefined ranges (step 1318). Such a divergence could, for example,indicate either that the sensor responsible for measuring the parameterhas malfunctioned or that condition of the applicable unit of equipmenthas significantly degraded.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that the specificdetails are not required in order to practice the invention. In otherinstances, well-known circuits and devices are shown in block diagramform in order to avoid unnecessary distraction from the underlyinginvention. Thus, the foregoing descriptions of specific embodiments ofthe present invention are presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, obviously many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated. It is intended that the following Claimsand their equivalents define the scope of the invention.

1-18. (canceled)
 19. A method for monitoring condition of equipment usedto effect a process, said method comprising: formulating a model of saidprocess, said model including at least a first maintenance parameter;and adjusting a value of said first parameter such that a predictedvalue of a process parameter of said process is reconciled with ameasured value of said process parameter derived from measurements ofcharacteristics of said process; and monitoring changes in said value ofsaid first maintenance parameter over time wherein changes in said valueare indicative of changes in said condition of said equipment.
 20. Themethod of claim 19 further including measuring flow rates of at leastfirst and second of said resource flows in order to generate respectivefirst and second measured resource flow signals wherein said model isbased upon conservation of said process parameter and said processparameter characterizes said first and second resource flows.
 21. Themethod of claim 20 wherein said model is further based upon a secondmaintenance parameter, said adjusting including modifying a value ofsaid second maintenance parameter and said monitoring including trackingchanges in said value of said second maintenance parameter.
 22. A methodfor monitoring condition of a plurality of units of equipment used toeffect a process involving one or more resource flows, said methodcomprising: measuring flow rates of at least first and second of saidresource flows in order to generate respective first and second measuredresource flows; formulating a model of said process, said modelincluding a plurality of nonlinear equipment models corresponding tosaid plurality of units of equipment wherein at least a first of saidnonlinear equipment models includes a first maintenance parameter;adjusting a value of at least said first maintenance parameter such thatpredictions of said flow rates are reconciled with said first and secondmeasured resource flows; and monitoring changes in said value of saidfirst maintenance parameter over time in order to enable detection ofchanges in condition of at least one of said plurality of units ofequipment.
 23. The method of claim 22 wherein at least a second of saidnonlinear equipment models includes a second maintenance parameter, saidmethod including adjusting said second maintenance parameter andmonitoring changes in said second maintenance parameter over time. 24.The method of claim 19 wherein the monitoring further comprisesmonitoring the first maintenance parameter over time to detect equipmentwear and anticipate equipment failure.
 25. The method of claim 19wherein said adjusting further comprises adjusting a first value of saidfirst measured resource flow signal and a second value of said secondmeasured resource flow signal, said adjusting minimizing a sum ofsquared difference values representative of error differentials in saidfirst and second measured resource flow signals.
 26. The method of claim25 wherein a weighting factor is assigned to each of said squareddifference values based upon accuracy of a corresponding sensor disposedto measure one of said flow rates.
 27. The method of claim 25 whereinsaid adjusting further comprises adjusting said first value by a firstoffset, adjusting said second value by a second offset, and providing auser indication of said first offset and second offset.
 28. The methodof claim 22 wherein the monitoring further comprises monitoring thefirst maintenance parameter over time to detect equipment wear andanticipate equipment failure.
 29. The method of claim 22 wherein saidadjusting further comprises adjusting a first value of said firstmeasured resource flow signal and a second value of said second measuredresource flow signal, said adjusting minimizing a sum of squareddifference values representative of error differentials in said firstand second measured resource flow signals.
 30. The method of claim 29wherein a weighting factor is assigned to each of said squareddifference values based upon accuracy of a corresponding sensor disposedto measure one of said flow rates.
 31. The method of claim 29 whereinsaid adjusting further comprises adjusting said first value by a firstoffset, adjusting said second value by a second offset, and providing auser indication of said first offset and second offset.
 32. Acomputer-based system for monitoring the condition of equipment used toeffect a process, said system comprising: a first sensor for measuring aflow rate of a first resource flow in order to generate a first measuredresource flow signal; a second sensor for measuring a flow rate of asecond resource flow in order to generate a second measured resourceflow signal; a model generation module operative to formulate a model ofsaid process based upon conservation of a process parametercharacterizing said first and second resource flows, said modelcomprising at least a first maintenance parameter; an adjustment moduleoperative to adjust at least the first maintenance parameter such thatpredictions of said flow rates are reconciled with said first and secondmeasured resource flows; a monitoring module operative to monitorchanges in said value of said first maintenance parameter over time inorder to enable detection of changes in condition of at least one unitof equipment of a plurality of units of equipment.
 33. The system ofclaim 32, the model further comprising a second maintenance parameter,said adjustment module modifying a value of said second maintenanceparameter.
 34. The system of claim 32 wherein the monitoring modulefurther monitors the first maintenance parameter over time to detectequipment wear and anticipate equipment failure.
 35. The system of claim32 wherein said adjustment module further adjusts a first value of saidfirst measured resource flow signal and a second value of said secondmeasured resource flow signal, said adjusting minimizing a sum ofsquared difference values representative of error differentials in saidfirst and second measured resource flow signals.
 36. The system of claim35 wherein a weighting factor is assigned to each of said squareddifference values based upon accuracy of a corresponding sensor disposedto measure one of said flow rates.
 37. The system of claim 35 whereinsaid adjusting further comprises adjusting said first value by a firstoffset, adjusting said second value by a second offset, and providing auser indication of said first offset and second offset.